* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'PingFang SC', 'Microsoft YaHei', sans-serif;
            background: linear-gradient(135deg, #DCF5D9 0%, #F8F9F7 100%);
            min-height: 100vh;
            color: #102620;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 20px;
        }

        .header {
            text-align: center;
            margin-bottom: 30px;
            background: rgba(255, 255, 255, 0.9);
            padding: 25px;
            border-radius: 20px;
            box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
        }

        .main-title {
            font-size: 36px;
            color: #004737;
            margin-bottom: 15px;
            font-weight: bold;
        }

        .subtitle {
            font-size: 22px;
            color: #636D6A;
            margin-bottom: 20px;
        }

        .teaching-content {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 30px;
            margin-bottom: 30px;
        }

        .story-section, .interactive-section {
            background: rgba(255, 255, 255, 0.95);
            padding: 25px;
            border-radius: 15px;
            box-shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
        }

        .section-title {
            font-size: 24px;
            color: #004737;
            margin-bottom: 20px;
            border-left: 4px solid #A7DB9A;
            padding-left: 15px;
        }

        .story-image {
            width: 100%;
            max-width: 300px;
            height: 200px;
            object-fit: cover;
            border-radius: 10px;
            margin: 15px 0;
            display: block;
            margin-left: auto;
            margin-right: auto;
        }

        .question-chain {
            background: #AACA9F;
            color: white;
            padding: 15px;
            border-radius: 10px;
            margin: 15px 0;
            font-size: 18px;
            font-weight: bold;
        }

        .measurement-methods {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 20px;
            margin: 20px 0;
        }

        .method-card {
            background: #F8F9F7;
            padding: 20px;
            border-radius: 12px;
            border: 2px solid #A7DB9A;
            text-align: center;
        }

        .method-title {
            font-size: 20px;
            color: #004737;
            margin-bottom: 15px;
            font-weight: bold;
        }

        .circle-demo {
            width: 200px;
            height: 200px;
            margin: 20px auto;
            position: relative;
        }

        .circle {
            width: 100%;
            height: 100%;
            border: 4px solid #FF6421;
            border-radius: 50%;
            position: relative;
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .circle:hover {
            transform: scale(1.05);
            border-color: #FF9364;
        }

        .diameter-line {
            position: absolute;
            top: 50%;
            left: 10%;
            right: 10%;
            height: 2px;
            background: #FFDE5E;
            transform: translateY(-1px);
            opacity: 0;
            transition: opacity 0.5s ease;
        }

        .diameter-label {
            position: absolute;
            bottom: -25px;
            left: 50%;
            transform: translateX(-50%);
            background: #FFDE5E;
            padding: 5px 10px;
            border-radius: 15px;
            font-size: 16px;
            font-weight: bold;
            opacity: 0;
            transition: opacity 0.5s ease;
        }

        .circumference-highlight {
            position: absolute;
            top: -4px;
            left: -4px;
            right: -4px;
            bottom: -4px;
            border: 4px dashed #FF6421;
            border-radius: 50%;
            opacity: 0;
            animation: rotate 3s linear infinite;
            transition: opacity 0.5s ease;
        }

        @keyframes rotate {
            from { transform: rotate(0deg); }
            to { transform: rotate(360deg); }
        }

        .controls {
            text-align: center;
            margin: 20px 0;
        }

        .btn {
            background: #A7DB9A;
            color: #004737;
            border: none;
            padding: 12px 25px;
            margin: 5px;
            border-radius: 25px;
            font-size: 18px;
            font-weight: bold;
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .btn:hover {
            background: #004737;
            color: white;
            transform: translateY(-2px);
        }

        .btn:active {
            transform: translateY(0);
        }

        .measurement-display {
            background: #DCF5D9;
            padding: 20px;
            border-radius: 12px;
            margin: 20px 0;
            text-align: center;
        }

        .measurement-value {
            font-size: 24px;
            color: #004737;
            font-weight: bold;
            margin: 10px 0;
        }

        .formula-section {
            background: rgba(255, 222, 94, 0.2);
            padding: 25px;
            border-radius: 15px;
            margin: 20px 0;
            border: 2px solid #FFDE5E;
        }

        .formula-display {
            text-align: center;
            font-size: 28px;
            margin: 20px 0;
            padding: 15px;
            background: white;
            border-radius: 10px;
        }

        .practice-section {
            background: rgba(255, 100, 33, 0.1);
            padding: 25px;
            border-radius: 15px;
            margin: 20px 0;
            border: 2px solid #FF6421;
        }

        .practice-problem {
            background: white;
            padding: 20px;
            border-radius: 10px;
            margin: 15px 0;
            border-left: 4px solid #FF6421;
        }

        .input-group {
            margin: 15px 0;
            text-align: center;
        }

        .input-group label {
            display: block;
            margin-bottom: 8px;
            font-size: 18px;
            font-weight: bold;
            color: #004737;
        }

        .input-group input {
            padding: 10px;
            border: 2px solid #A7DB9A;
            border-radius: 8px;
            font-size: 18px;
            text-align: center;
            width: 120px;
        }

        .result-display {
            background: #DCF5D9;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
            text-align: center;
            font-size: 20px;
            font-weight: bold;
            color: #004737;
        }

        .progress-bar {
            width: 100%;
            height: 8px;
            background: #F8F9F7;
            border-radius: 4px;
            margin: 20px 0;
            overflow: hidden;
        }

        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, #A7DB9A, #AACA9F);
            width: 0%;
            transition: width 0.5s ease;
        }

        .step-indicator {
            display: flex;
            justify-content: space-between;
            margin: 20px 0;
        }

        .step {
            flex: 1;
            text-align: center;
            padding: 10px;
            background: #F8F9F7;
            margin: 0 5px;
            border-radius: 20px;
            font-size: 16px;
            font-weight: bold;
            color: #636D6A;
            transition: all 0.3s ease;
        }

        .step.active {
            background: #A7DB9A;
            color: #004737;
        }

        .step.completed {
            background: #004737;
            color: white;
        }

        .footer {
            background: linear-gradient(to right);
            color: #0c0302;
            text-align: center;
            padding: 10px;
            margin-top: 15px;
            border-radius: 0 0 10px 10px;
        }

        .hidden {
            display: none;
        }

        .fade-in {
            animation: fadeIn 0.8s ease-in;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(20px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .wheel-animation {
            width: 150px;
            height: 150px;
            border: 6px solid #8B4513;
            border-radius: 50%;
            margin: 20px auto;
            position: relative;
            animation: wheelSpin 4s linear infinite;
        }

        .wheel-animation::before {
            content: '';
            position: absolute;
            top: 50%;
            left: 50%;
            width: 20px;
            height: 20px;
            background: #654321;
            border-radius: 50%;
            transform: translate(-50%, -50%);
        }

        @keyframes wheelSpin {
            from { transform: rotate(0deg); }
            to { transform: rotate(360deg); }
        }

        .spokes {
            position: absolute;
            top: 50%;
            left: 50%;
            width: 2px;
            height: 60px;
            background: #654321;
            transform-origin: bottom center;
        }

        .spoke-1 { transform: translate(-50%, -100%) rotate(0deg); }
        .spoke-2 { transform: translate(-50%, -100%) rotate(45deg); }
        .spoke-3 { transform: translate(-50%, -100%) rotate(90deg); }
        .spoke-4 { transform: translate(-50%, -100%) rotate(135deg); }
        .spoke-5 { transform: translate(-50%, -100%) rotate(180deg); }
        .spoke-6 { transform: translate(-50%, -100%) rotate(225deg); }
        .spoke-7 { transform: translate(-50%, -100%) rotate(270deg); }
        .spoke-8 { transform: translate(-50%, -100%) rotate(315deg); }

        @media (max-width: 768px) {
            .teaching-content {
                grid-template-columns: 1fr;
            }
            
            .measurement-methods {
                grid-template-columns: 1fr;
            }
            
            .main-title {
                font-size: 28px;
            }
            
            .subtitle {
                font-size: 18px;
            }
        }